An organic electroluminescent (hereinafter abbreviated to “EL” when appropriate) device has a multilayer structure comprising (i) a luminescent layer comprising a light emitting material and (ii) a hole transport layer and an electron transport layer, which sandwich the luminescent layer, and (iii) an anode and a cathode, which sandwich the hole transport layer, the luminescent layer and the electron transport layer. The organic EL device utilizes light emission (fluorescence or phosphorescence) occurring at deactivation of an exciton formed by the recombination of electron with hole, which are injected in the luminescent layer. The organic EL device is widely used for a display and other applications.
Patent documents 1 and 2 disclose organic EL device containing a pyrimidine compound as a luminescent material. The pyrimidine compound includes those which have a substituted phenyl substituent at a 2-position in the pyrimidine ring, but, the positions at which substituents are bonded to the phenyl substituent are not limited. These patent documents are silent on pyrimidine compounds having a substituted phenyl substituent at a 2-position in the pyrimidine ring, which has two specific substituents at 3- and 5-positions of the phenyl substituent. Thus, these patent documents are silent on a pyrimidine compounds of the formula (1a), described below, of the present invention which has a substituted phenyl substituent at a 2-position in the pyrimidine ring, which has two specific substituents at 3- and 5-positions of the phenyl substituent.
Patent documents 3 and 4 disclose an organic EL device containing a pyrimidine compound having a 4-substituted phenyl substituent. However, these documents are silent on a pyrimidine compound of the formula (1a), described below, of the present invention which has a substituted phenyl substituent at a 2-position in the pyrimidine ring, which has two specific substituents at 3- and 5-positions of the phenyl substituent.
Patent document 5 discloses an organic EL device containing a pyrimidine compound having a phenyl group condensed with an aromatic hetero 5-membered ring. However, this document is silent on a pyrimidine compound of the formula (1a), described below, of the present invention which has a substituted phenyl substituent at a 2-position in the pyrimidine ring, which has two substituents at 3- and 5-positions of the phenyl substituent.
Patent document 6 discloses an organic EL device containing a pyrimidine compound. As one example of the pyrimidine compounds, a pyrimidine compound having a substituted phenyl substituent at 2-position of the pyrimidine ring, wherein the phenyl substituent has two phenyl groups at 3- and 5-positions of the phenyl substituent. The two phenyl groups at 3- and 5-positions thereof have no substituent. In contrast, the pyrimidine compounds of the formula (1a), described below, of the present invention has a substituted phenyl substituent at a 2-position in the pyrimidine ring, which has two specific substituents at 3- and 5-positions of the phenyl substituent, wherein each substituent is a phenyl group having a substituent or a condensed aromatic hydrocarbon group. Thus, the pyrimidine compound disclosed in patent document 6 is distinguished from the pyrimidine compound of the formula (1a). The pyrimidine compound disclosed in patent document 6 is also distinguished from the pyrimidine compound of the formula (1c), described below, of the present invention.
Patent document 7 discloses an organic EL device containing a pyrimidine compound. This pyrimidine compound has no polycyclic aromatic group, and thus, is distinguished from the pyrimidine compounds of the formulae (1b) and (1c) of the present invention.
Patent documents 8 and 9 disclose an organic EL device containing 1,3,5-triazine compounds having polycyclic aromatic groups. The triazine compounds are characterized as exhibiting a structural isomerism occurring steric hindrance, and thus, these compounds are distinguished from the pyrimidine compounds of the formulae (1b) and (1c) of the present invention. In patent document 8, there is no working example wherein a 1,3,5-triazine compound having a phenyl group bonded to the triazine ring, said phenyl group having two aromatic hydrocarbon groups each having 2 to 4 rings. Further the two patent documents 8 and 9 suggest nothing about the glass transition temperature (Tg) and electron mobility of the triazine compound.
More specifically patent documents 8 and 9 give only working examples wherein 1,3,5-triazine compounds having the same substituents at 2-, 4- and 6-positions thereof are described, and any description of glass transition temperature (Tg) is not specifically given.
For the use as a basic material of an organic EL device, a thin film of the basic material must be amorphous and have smooth surface. A triazine compound having a highly symmetrical skeletal is highly crystalline, therefore, unsatisfactory for the basic material of the EL device. The cyclic azine compound of the formula (1d), described below, of the present invention has a structure such that different substituents are arranged at 2-, 4- and 6-positions of a 1,3,5-triazne ring, and thus crystallization of a thin film of the cyclic azine compound is controlled. The cyclic azine compound of the present invention has characteristics occurring due to the molecule skeletal which are distinguished from those of the triazine compound having a symmetrical skeletal.
Patent document 10 discloses a nitrogen-containing heterocyclic compound for use in an organic EL device. As one example of the heterocyclic compound, a compound having a 1,3,5-triazine ring and a pyrenyl group is mentioned (Table 12, No. 6-13). However, any specific explanation of this compound and working example thereof are not given, and Tg and electron mobility thereof are not mentioned.
Patent documents 9 and 11 disclose a cyclic azine compound, i.e., 1,3,5-triazine compound for use in an organic EL device. This triazine compound includes those which have substituted phenyl groups at 2-, 4- and 6-positions of the triazine ring, but, the positions of the substituents of the phenyl groups are not limited. These patent documents are silent on the cyclic azine compound of the formula (1c) of the present invention, said azine compound having a phenyl group at 2-position of the triazine ring, which phenyl group has 3,5-di-substituted phenyl groups or 2,6-di-substituted pyridyl groups.